Tunable resonator

ABSTRACT

The gas turbine engine including, in serial flow communication, a compressor, a combustor, a turbine, and a fluid system fluidly connecting at least two components of the gas turbine engine, also includes a tunable resonator in fluid flow communication with the fluid system, the tunable resonator. The tunable resonator has a resonating volume that varies as a function of a volume of an inflatable member located inside the tunable resonator. The inflatable member having a means for varying the volume of the inflatable member, to thereby tune the resonating volume to a selected frequency of pressure fluctuations or acoustic waves within the fluid system.

TECHNICAL FIELD

The application relates generally to gas turbine engine fluid systemsand, more particularly, to resonators used to attenuate or dump pressurefluctuations or acoustic waves in such fluid systems.

BACKGROUND

Gas turbine engines are operated over a wide range of operatingconditions and are required to handle various flow conditions duringoperation. The fluid-structure-acoustic interactions that occur in fluidsystems of such engines can exhibit resonances or pressure fluctuationsresulting in undesirable consequences, such as noise generation,vibratory stresses, etc. The amplitude and frequency of the excitationor the undesirable noise vary with a number of parameters, including theoperating and/or flow conditions, and configuration of the relatedcomponents of the fluid systems.

Resonators have been used to mitigate the noise and associated stress onthe affected components. A conventional single resonator design is tunedto a specific target frequency, and therefore it is effective but onlyover a narrow range of frequencies. However, the target frequency of thegenerate noise can sometimes change quite significantly with enginepower or varied operating and/or flow conditions. Hence, in an effort toattenuate or dump pressure fluctuations or acoustic waves over a rangeof frequencies, several customized resonators can sometimes be requiredto cover those frequencies, thereby adding undesirable cost and weightto the engine.

SUMMARY

There is accordingly provided a tunable resonator for damping at leastone selected frequency of pressure fluctuations or acoustic waves withina fluid system of a gas turbine engine, the tunable resonatorcomprising: an outer casing enclosing a chamber defining a total innervolume and having an inlet therein configured to provide fluid flowcommunication between the chamber and the fluid system, the outer casingdefining an axial direction and a radial direction; and an inflatablemember disposed within the outer casing adjacent at least one inner wallof the outer casing, the inflatable member having a skin defining asub-chamber within the chamber, the skin configured to prevent fluidflow between the sub-chamber and the chamber, the skin being deformablebetween a deflated position and one or more inflated positions to changea volume of the sub-chamber; wherein a resonating volume of the tunableresonator corresponds to a difference between the total inner volume ofthe chamber and the volume of the sub-chamber.

There is also provided a gas turbine engine comprising, in serial flowcommunication, a compressor, a combustor, and a turbine, the gas turbineengine further having a fluid system fluidly connecting at least twocomponents of the gas turbine engine and including a tunable resonatorin fluid flow communication with the fluid system, the tunable resonatordefining an axial direction and a radial direction, the tunableresonator having a resonating volume that varies as a function of avolume of an inflatable member located inside the tunable resonator, theinflatable member having a means for varying the volume, the inflatablemember thereby tuning the resonating volume to a selected frequency ofpressure fluctuations or acoustic waves within the fluid system.

There is further provided a method for tuning a resonator in a fluidsystem of a gas turbine engine, the method comprising: determining afrequency of pressure fluctuations or acoustic waves occurring in thefluid system; determining a required resonating volume of the resonatorfluidly connected to the fluid system for damping the pressurefluctuations or acoustic waves; and changing a resonating volume of theresonator by deforming one or more walls of an inflatable member untilthe resonating volume corresponds to the required resonating volume.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures in which:

FIG. 1 is a schematic cross-sectional view of a gas turbine engine;

FIG. 2a is a schematic cross-sectional view of a tunable resonator inaccordance with a particular embodiment;

FIG. 2b is a schematic cross-sectional view of a tunable resonator inaccordance with a particular embodiment;

FIG. 2c is a cross-sectional view taken along line 2 c-2 c of FIGS. 2aand 2 b;

FIGS. 3a to 3d are schematic tridimensional views of an inflatablemember of the tunable resonators of FIGS. 2a to 2c , the inflatablemember is shown in different inflated positions;

FIG. 4a is a schematic front view of a portion of a skin of theinflatable member of FIG. 3a ; and

FIG. 4b is a schematic cross-sectional view taken along line 4 b-4 b onFIG. 4 a.

DETAILED DESCRIPTION

FIG. 1 illustrates a gas turbine engine 10 of a type preferably providedfor use in flight, generally comprising in serial flow communication afan 12 through which ambient air is propelled, a compressor section 14for pressurizing the air, a combustor 16 in which the compressed air ismixed with fuel and ignited for generating an annular stream of hotcombustion gases, and a turbine section 18 for extracting energy fromthe combustion gases. The gas turbine engine further comprises a case 20defining an annular by-pass conduit 22 surrounding the compressor 14,the combustor 16, and the turbine 18. Although the engine 10 is shown asa turbofan, the disclosure of the present application may be applied toother types of engines, such as, but not limited to, turboprops andturboshafts.

The gas turbine engine 10 further has a fluid system 30. The fluidsystem 30 may be used to direct air between two components. Such fluidsystems 30 may include, but are not limited to, air, oil, fuel and/orhydraulic systems of the engine. Additionally, the resonators asdescribed herein may also be used to reduce structural damage due topressure pulses from vane pumps or to reduce surges due toopening/closing of valves. In certain operating and/or flow conditions,the air or fuel lines or ducts of the fluid system 30 can exhibit highpressure fluctuations caused by, for example only, pumps, valves,vortices, etc., and which may be directly or indirectly responsible forthe generation of unwanted noise. In some cases, resonance can occur ata given frequency. Such pressure fluctuations and/or acoustic wavescausing noise generation can be of the fluid-acoustics interaction inthe cavities or pipes of the system, which can sometimes lead to thecavities or pipes entering into resonances, or causingfluid-structure-acoustic interactions where the noise or acousticexcitation is sustained thereby causing high stress on the relatedcomponents.

In the illustrated embodiment, a resonator 32 in fluid communicationwith the fluid system 30 is used to dampen one or more selectedfrequencies of pressure fluctuations or acoustic waves occurring in thefluid system 30. The resonator 32 typically comprises a resonatingvolume that is pre-selected to dampen the pressure fluctuations oracoustic waves. The more generic term “vibrations” may also be usedherein to refer to such pressure fluctuations and/or acoustic wavesoccurring in the fluid.

Still referring to FIG. 1, the fluid system 30 comprises a conduit 34fluidly connecting at least two components of the gas turbine engine 10.In the illustrated embodiment, the two components are a scoop 36 and acase 38 of the turbine section 18 requiring cooling. The scoop 36 isused to bleed air from the annular by-pass conduit 22, downstream of thefan 12 relative to an annular flow 40 circulating in the by-pass conduit22. The bled air may be used to cool the turbine case 38. The resonator32 is affixed to the conduit 34, between the scoop 36 and the turbinecase 38. The resonator 32 is hence fluidly connected to the conduit 34.It is however understood that the use of the disclosed fluid system 30and the arrangement disclosed herein are only one of many possiblearrangements and uses.

As aforementioned, the resonator 32 can only dampen one frequency, or anarrow range of frequencies, and may therefore become purposeless whenthe given frequency shifts. The reasons for such a shift are typically achange in the operating conditions of the gas turbine engine 10. In aparticular embodiment, the operating conditions are the outsidetemperature—which can vary by approximately 200 degrees Fahrenheit—athrust level of the gas turbine engine 10, the rotational speed of acomponent of the engine (e.g. compressor 14 and turbine 18, and moreparticularly one or more of the Low Pressure (LP) shaft, the HighPressure (HP) shaft and/or the Intermediate Pressure (IP) shaft), a massflow rate in the fluid system 30, and/or pressure ratios in the fluidsystem 30. Other factors may also influence the frequency, includingaltitude. Therefore, to cater to the different possible frequencies, itmay become necessary to add more resonators to the fluid system 30,which adds weight to the engine 10.

One option to tune the resonator 32 to dampen pressure fluctuationsand/or acoustic waves occurring at another frequency is to vary itsresonating volume. By doing so, the frequency of the pressurefluctuations and/or acoustic waves that the resonator is adapted todampen can be varied in function of the operating conditions of the gasturbine engine 10. The resonator 32 may be a Helmholtz resonator 100 andan in-line resonator 200, or any derivatives and/or combinationsthereof, both of which are discussed in further details herein below.

Now referring to FIG. 2a , in the in-line resonator 100, the flow F′circulating therein is parallel to a flow F circulating in the conduit34 of the fluid system 30. The resonator 100 has an outer casing 102 ofa length Lc longitudinally extending along an axis L extending parallelto the conduit 34. The outer casing 102 has an inlet 104 and an outlet106. The inlet 104 and the outlet 106 are fluidly connected to theconduit 34 of the fluid system 30. The outer casing 102 encloses achamber 108 that has an inner volume. In such a case, a resonatingvolume of the resonator 100 corresponds to the inner volume of thechamber 108.

Now referring to FIG. 2b , in the Helmholtz resonator 200, the flow Fcirculating in the conduit 34 is perpendicular to the flow F″circulating in the resonator 200. The resonator 200 has an outer casing202 of a length Lc′ longitudinally extending along an axis L′ extendingperpendicularly to the conduit 34. The outer casing 202 has a combinedinlet and outlet 204 configured to be fluidly connected to the conduit34 of the fluid system 30. In the illustrated embodiment, the resonatorouter casing 202 encloses a chamber 206 that has an inner volume.Similarly to the embodiment depicted in FIG. 2a , a resonating volume ofthe resonator 200 corresponds to the volume of the chamber 206. Theresonator 200 further comprises a neck 208 of a length Ln extendingalong the axis L′. The neck 208 has a given cross-sectional area. Theneck 208 fluidly connects the chamber 206 to the fluid conduit 34.

Referring concurrently to FIGS. 2a and 2b , the frequency of thepressure fluctuations and/or acoustic waves that the resonator 100 or200 is adapted to dampen is function of a plurality of geometricparameters, such as, but not limited to, the speed of sound, theresonating volume, the cross-sectional area of the neck 208, and thelength Ln of the neck 208. Hence, as aforementioned, by modifying theresonating volume it is possible to tune the resonator 100/200 to dampenpressure fluctuations and/or acoustic waves occurring at anotherfrequency without changing its geometric characteristics. In theillustrated embodiment, an inflatable member 50 is used for thatpurpose.

Referring also to FIG. 2c , the inflatable member 50 is inserted in theouter casing 102/202 of the resonator 100/200. In the illustratedembodiment, the inflatable member 50 is adjacent inner walls 110/210 ofthe outer casing 102/202. The inflatable member 50 has a skin 52defining a sub-chamber 54 therewithin. The skin 52 prevents fluidcommunication between the chamber 108/206 and the sub-chamber 54. Theskin 52 of the inflatable member 50 is deformable between a deflatedposition and one or more inflated positions. The deflated position ofthe inflatable member 50 has a deflated volume. In a particularembodiment, the deflated volume is negligible such that the resonatingvolume corresponds to the total inner volume of the chamber 108/206.More details regarding the deformation of the inflatable member 50 areprovided herein below.

By providing the inflatable member 50 inside the chamber 108/206 of theouter casing 102/202, the resonating volume may be varied. Theresonating volume thereby corresponds to a difference between the volumeof the chamber 108/206 and the volume of the sub-chamber 54.

Referring more particularly to FIG. 2c , the inflatable member 50 maycomprise two sub-members 50 a and 50 b each extending along half aperimeter of the outer casing 102/202 and enclosing a respectivesub-chamber 54 a/b. In the illustrated embodiment, each of the twosub-members 50 a/b takes the form of a half of a cylinder. The twosub-members 50 a/b are disposed to abut against one another alongabutting walls 60 thereof such that the inflatable sub-members 50 a/btake the form of a cylinder. In a particular embodiment, the inflatablemember 50 comprises one sub-member. The inflatable member 50 maycomprise more than two sub-members. The sub-members 50 a/b may beaxially and/or radially deformable to vary the volume of the sub-chamber54 a/b and hence the resonating volume. Accordingly, the resonatingvolume varies inversely to the volume of the sub-chambers 54 a/b. Thisaspect is discussed below. The inflatable sub-member 50 a is describedin further detail below. It is understood that the characteristics ofthe sub-member 50 a may be the same for the sub-member 50 b.

Referring now to FIG. 3a , the skin 52 of the inflatable sub-member 50 ais shaped to define half a cylinder having a radially-inner wall 62, aradially-outer wall 64, an annular proximal wall 66, and an annulardistal wall 68. In a particular embodiment, the radially-outer wall 64is affixed to the inner wall 110/210 of the outer casing 102/202.Although the inflatable member 50 a has been depicted as cylindrical, itis understood that other shapes may be used without departing from thescope of the present disclosure.

Referring now to FIGS. 3a to 3d , the inflatable sub-member 50 a changesthe volume of its sub-chamber 54 a by expansion/retraction along anaxial direction A and/or a radial direction R. The inflatable member ina deflated position is schematically illustrated in FIG. 3a . In aparticular embodiment, the two sub-members 50 a and 50 b can besimultaneously or independently inflatable relative to one another.

Referring more particularly to FIG. 3b , in one embodiment, theinflatable sub-member 50 a changes the resonating volume byexpansion/retraction along the axial direction A. In the illustratedembodiment, the inflatable sub-member 50 a longitudinally extends fromthe deflated position P0 to one inflated position P1 illustrated indashed lines. When the inflatable sub-member 50 a is inserted in thechamber 108/206 of the resonator 100/200, its length Lm increases ordecreases. For the in-line resonator 100 of FIG. 2a , the length Lmextends parallel to the flow F that circulates in the fluid conduit 34of the fluid system 30. For the Helmholtz resonator 200, the length Lmextends perpendicularly to the flow F. In the illustrated embodiment,the sub-member 50 a can expand until both the proximal and distalannular walls 66 and 68 abut against the inner walls 110/210 of theouter casing 102/202.

Referring more particularly to FIG. 3c , the inflatable sub-member 50 achanges the resonating volume by expansion/retraction along the radialdirection R. The inflatable sub-member 50 a is deformable between thedeflated position P0 and another inflated position P2 illustrated indashed lines. The inflatable sub-member 50 a may cover only a portion ofthe length Lc of the outer casing 102/202.

In a particular embodiment, the inflatable sub-member 50 a can expanduntil the radially-outer wall 64 abuts against the inner walls 110/210of the outer casing 102/202 and until an inner radius Ri of theradially-inner wall 62 becomes substantially negligible. In the case ofthe in-line resonator 100, the inflatable member 50 may therefore beconfigured as a valve adapted to block the flow in the fluid conduit 34of the fluid system 30.

Now referring to FIG. 3d , the inflatable sub-member 50 a changes theresonating volume by expansion/retraction along both the radial R andaxial A directions. The inflatable member 50 is therefore deformablebetween the deflated position P0 and an inflated position P3 alsoillustrated in dashed lines. Similarly to the embodiment depicted inFIG. 3c , the sub-member 50 a may be configured to block the flowcirculating in the fluid conduit 34 of the fluid system 30. In theillustrated embodiment, the sub-member 50 a can expand until both theproximal and distal annular walls 66 and 68 abut against the inner walls110/210 of the outer casing 102/202.

In the illustrated embodiments, the resonating volume is greater whenthe inflatable member 50 is in the deflated position P0 than when theinflatable member 50 is in any of the depicted inflated positions P1,P2, and P3.

To be able to move from the deflated position to any of the inflatedpositions, the inflatable member 50 has a mean to vary the volume of itssub-chamber 54. One of the possible means is discussed below. In aparticular embodiment, the mean would be similar to the morphingmaterials disclosed in U.S. Pat. No. 9,415,856, the entire content ofwhich is enclosed herein by reference. The inflatable member 50 maycomprise ribs whose positions are changed with an actuator to change theshape and the volume of the sub-chamber 54.

In a particular embodiment, the mean would be similar to the layer offibers disclosed in U.S. Pat. No. 7,195,210, the entire content of whichis enclosed herein by reference. The skin 52 of the inflatable member 50may comprise the layer of fibers embedded therein. The fibers comprise afirst set of fibers extending in a first direction and a second set offibers extending in a second direction. The first and second directionsdefining an angle that is variable with a change of volume of thesub-chamber 54.

In a particular embodiment, the mean would be similar to the morphingstructure disclosed in U.S. Pat. No. 8,991,769, the entire content ofwhich is enclosed herein by reference. The inflatable member 50 maycomprise the morphing structure adjacent the skin 52. The morphingstructure includes a plurality of morphing elements. Each morphingelement comprises four rigid members. Both ends of each of the rigidmembers are pivotally mounted to and end of another rigid members usinghinges thereby forming a closed figure (e.g. square). The morphingstructure further comprises two springs. Each spring is attached to twoopposed hinges such that an angle between two consecutive rigid membersis 90 degrees when no force is exerted on the morphing element. Theangle variable with a change of volume of the inflatable member.

In another particular embodiment, the mean would be similar to the smartmaterial disclosed in U.S. Pat. No. 9,457,887, the entire content ofwhich is enclosed herein by reference. The skin 52 of the inflatablemember may be made of the smart material, or be affixed to the smartmaterial. The smart material is capable of changing its shape throughapplication of a stimulus. The stimulus may be light, heat, electricvoltage/current, magnetic fields, pressure variation, and a combinationthereof. The smart material may be piezoelectric composites,electro-active polymers, shape memory alloys, and carbon nanotubecomposites. In yet another particular embodiment, a portion of the skin52 of the inflatable member 50 is made of Veriflex™ Veritex™, Verilyte™,and/or Flex-foil™. In a particular embodiment, the skin 52 is disposedadjacent a structure made of the above listed materials.

Now referring to FIGS. 4a and 4b , a portion of the skin 52 of theinflatable member 50 has a plurality of panels 80. Two successive panels80 are pivotable relative to one another along an edge 82 joining thetwo panels 80 to define a gusset 84. In the illustrated embodiment, theedge 82 is deformable. In a particular embodiment, the edge 82 is ahinge joining the two successive panels 80. In the illustratedembodiment, the skin 52 comprises a plurality of gussets 84 to define anaccordion section 86 of the inflatable member skin 52.

Referring more particularly to FIG. 4b , the two successive panels 80define an angle α that is variable in function of the volume of thesub-chamber 54 of the inflatable member 50. In the illustratedembodiment, the angle α varies from 0 degree, in the deflated positionP0 (see FIG. 3), to 180 degrees in a fully inflated position. Thedirection of elongation D is therefore perpendicular to the edges 82.The walls 60, 62, 64, 66, and 68 that require deformation to allow axialand/or radial expansion/retraction of the inflatable member 50 areprovided with the above described gussets 84. In a particularembodiment, the walls are provided with the alternate means that havebeen described hereinabove.

In a particular embodiment, the skin 52 comprises a plurality ofbuilding blocks arranged in a lattice to give morphing properties to theskin 52 of the inflatable member 50. One of the building blocks maycomprise the structure illustrated on FIGS. 4a and 4b . The skin 52 maybe made of advanced composites, plastics, resins, polymers (e.g.neoprene-rubber), metals, and a combination thereof.

The frequency of the pressure fluctuations and/or acoustic waves thatthe resonator 100/200 is adapted to dampen may increases with a decreasein the resonating volume. In this case, the smaller the resonatingvolume, the greater is the frequency of the pressure fluctuations and/oracoustic waves that the resonator 100/200 is adapted to dampen. In otherwords, the greater the volume of the sub-chamber 54 of the inflatablemember 50, the greater is the frequency of pressure fluctuations and/oracoustic waves that the resonator 100/200 is adapted to dampen.

For tuning the resonator 100/200, the frequency at which the fluidsystem 30 oscillates, i.e. due to the pressure fluctuations and/oracoustic waves, is determined. This may be done either experimentally orby numerical analysis using computational fluid dynamics, for example. Arequired resonating volume for a range of operation and/or flowconditions is then computed. The resonating volume is then changed bydeforming one or more walls 60, 62, 64, 66, and 68 of the inflatablemember 50 until the resonating volume corresponds to the requiredresonating volume.

For the Helmholtz resonator 200, the required resonating volume isfunction of the frequency (fh) of the fluid system 30, the speed ofsound (v), the cross-sectional area (A) of the neck 208 fluidlyconnecting the resonator 200 to the fluid system 30, and the length (Ln)of the neck 208. In a particular embodiment, the required resonatingfrequency is determined by the equation, in its simpler form:

$f_{H} = {\frac{v}{2\; \pi}\sqrt{\frac{A}{V_{0}L_{eq}}}}$

For the in-line resonator 100, and in accordance with a particularembodiment, the required dimensions are determined by a complex functionof the chamber length Lc, element lengths, and the expansion ratio ofthe resonator.

In a particular embodiment, changing the resonating volume compriseschanging the angle α between the two sections 80 of at least one gusset84 of the skin 52 of the inflatable member 50. In the illustratedembodiment, the inflatable member 50 is inflated using compressed airfrom the compressor 14 of the engine.

In a particular embodiment, a controller (not shown) is used to monitorchanges in the frequency. Therefore, the controller comprises afrequency determining volume. The controller may be the engine controlsystem. The controller may further comprise an inflatable membercontrolling module for controlling the inflation/deflation of theinflatable member 50.

In a particular embodiment, a trigger to initiate deflation or inflationof the inflatable member 50 is a change in a flow parameter of the fluidsystem 30. The flow parameters may be the ambient temperature, therotational speed of a component of the gas turbine engine 10, a thrustlevel of the engine 10, a mass flow rate in the fluid system, and/or apressure ratio in the fluid system 30.

The above description is meant to be exemplary only, and one skilled inthe art will recognize that changes may be made to the embodimentsdescribed without departing from the scope of the invention disclosed.Still other modifications which fall within the scope of the presentinvention will be apparent to those skilled in the art, in light of areview of this disclosure, and such modifications are intended to fallwithin the appended claims.

1. A tunable resonator for damping at least one selected frequency ofpressure fluctuations or acoustic waves within a fluid system of a gasturbine engine, the tunable resonator comprising: an outer casingenclosing a chamber defining a total inner volume and having an inlettherein configured to provide fluid flow communication between thechamber and the fluid system, the outer casing defining an axialdirection and a radial direction; and an inflatable member disposedwithin the outer casing adjacent at least one inner wall of the outercasing, the inflatable member having a skin defining a sub-chamberwithin the chamber, the skin configured to prevent fluid flow betweenthe sub-chamber and the chamber, the skin being deformable between adeflated position and one or more inflated positions to change a volumeof the sub-chamber, the inflatable member including at least twoinflatable sub-members, the at least two inflatable sub-members eachcovering a portion of the at least one inner wall of the outer casing,the inflatable member in the one or more inflated positions, extendingradially relative to the radial direction of the outer casing, theinflatable member changing the volume of the sub-chamber by expansion orretraction in the radial direction; wherein a resonating volume of thetunable resonator corresponds to a difference between the total innervolume of the chamber and the volume of the sub-chamber.
 2. (canceled)3. The tunable resonator according to claim 1, wherein the tunableresonator is a Helmholtz resonator, a fluid passage of the fluid systembeing substantially perpendicular to a fluid passage of the tunableresonator.
 4. The tunable resonator according to claim 1, wherein thetunable resonator is an in-line resonator, a fluid passage of the fluidsystem being substantially parallel to a fluid passage of the tunableresonator.
 5. The tunable resonator according to claim 1, wherein aportion of the skin of the inflatable member has at least one gusset,the at least one gusset having two sections pivotable relative to oneanother along an edge joining the two sections, an angle between the twosections variable with a change of volume of the sub-chamber.
 6. Thetunable resonator according to claim 5, wherein the skin has a pluralityof gussets, the plurality of gussets defining an accordion section ofthe skin of the inflatable member.
 7. The tunable resonator according toclaim 1, wherein the inflatable member, in a fully inflated position,blocks a fluid flow from entering the tunable resonator.
 8. The tunableresonator according to claim 1, wherein the inflatable member, in theone or more inflated positions, further extends axially relative to theaxial direction of the outer casing, the inflatable member changing thevolume of the sub-chamber by expansion or retraction in the axialdirection and the radial direction. 9.-20. (canceled)
 21. A gas turbineengine comprising, in serial flow communication, a compressor, acombustor, and a turbine, the gas turbine engine further having a fluidsystem fluidly connecting at least two components of the gas turbineengine, the fluid system including the tunable resonator as defined inclaim 1, the tunable resonator in fluid flow communication with thefluid system.